Abstract: The polarization properties of thin film Fabry-Prot filter is investigated by eigen method. With the increase of incident angle, the wavelengths of the transmission modes of s-polarized light and p-polarized light separate gradually, but the separation is small. The transmittance of the transmission mode of s-polarized light vibrates greatly and the transmittance of the transmission mode of p-polarized light vibrates little with the increase of incident angle. When the incident angle changes at the separation of 1/100, the wavelengths of the transmission mode of s-polarized light and p-polarized light keep unchanged and the transmittance of the transmission mode of s-polarized light changes significantly, while the transmittance of the transmission mode of p-polarized light changes very small. The polarization properties of film Fabry-Prot filter can play an important role in angle measurement.